Malignant transformation by the avian Rous sarcoma virus is induced by a viruscoded protein which plays no role in virus reproduction. Attempts have been made to identify the metabolic function of this protein in transformation. Characteristic morphological and metabolic features of transformed cells have been used as a basis for examining possible functions of the transforming protein and a virus mutant which induces temperature-dependent transformation has been useful in distinguishing between direct and indirect effects of the protein. Using these methods, we have been able to eliminate two general metabolic areas, monovalten cation transfers and glycosylation reactions, from consideration as directly involved in transformation. On the other hand, differences in cytoskeletal proteins have been observed, and the possibility that they may directly bear on the transformation process is being pursued.